This application is cross-referenced to application Ser. No. 09/816,982 xe2x80x9cAC Power System With Redundant AC Power Sourcesxe2x80x9d that is being filed simultaneously with the present application.
The present invention relates generally to lithium-ion battery systems, and more particularly to a distributed converter for balancing charge in a lithium-ion battery system.
A spacecraft may require the use of as many as four lithium-ion batteries and a typical lithium-ion battery has about thirty cell units. A common approach for charging and balancing charge in the batteries uses a power supply for each cell unit of each battery for a total of one hundred and twenty power supplies that are used on board a spacecraft.
This is a complex, and costly, approach to charging lithium-ion batteries, especially for space applications, which are highly sensitive to weight and packaging constraints and require extreme levels of reliability. The large number of components in the typical battery system adversely affects the reliability of the battery system and ultimately the satellite itself. There is a need for a low cost and effective method of charging the cell units and balancing the charge of the cell units of lithium-ion batteries used on board a spacecraft.
It is an object of the present invention to provide a method for charging and balancing the cells of a lithium-ion battery. It is another object of the present invention to reduce the cost and complexity of the charging and equalization system.
It is a further object of the present invention to provide reliable and efficient control of cell charge balancing, eliminating the need for a separate power supply and charger for each cell in a lithium-ion battery system.
The present invention is a system and method for charging and balancing charge in a lithium-ion battery having an array of cells. A single bulk charger is used for all of the cells in an array of cells. A controller controls a plurality of balancing switches based on a measured voltage for each cell. A redundant alternating-current power supply is used for the plurality of equalizing switches.
According to the method of the present invention, the battery is charged by the bulk charger at a high rate until one or more of the cells reaches a predetermined series threshold voltage. When the series threshold voltage is reached, the controller provides instructions as to whether to reduce or terminate the cell charging by the bulk charger. At this point in time, the redundant power supplies begin charging each cell individually through the balancing switches. The balancing switches will turn off as their respective cells reach a predetermined cell threshold voltage. Ultimately, each cell will be fully charged to an identical high charge state.
These and other features of the present invention will be better understood with regard to the following description, appended claims, and accompanying drawings.